In Neighbors, Efron leads the fray as Teddy, a fraternity president who initially charms, and ultimately torments, his yuppie next-door neighbors (Rogen and Rose Byrne), who have recently moved into a college town with their baby.

"At his best and worst he's sort of like a couple of my best friends," says Efron of Teddy. "He's never wrong. He's extraordinarily cocky. But (he) would take a bullet for you."

Hazing, kegs of beer, endless supplies of weed and sparsely clothed students fill the screen in the no-holds-barred comedy, but Efron, who had recently completed a stint in rehab for drugs and alcohol at the time of the shoot, relied only on Red Bull.

Still, "everyone was freaked out about how much I knew" about beer pong, he says, describing walking on set and surveying the party scene about to unfold.

"More cups!" he hollered, rearranging the classic red cups. "There (needs to be) liquor everywhere! Tons of people! More teams! More balls! Balls everywhere! This is how the game is played!"

On paper, Teddy was every mother's worst nightmare, with "not a redeemable quality about him," says Efron, who pushed for a more well-rounded villain. "Zac's whole thing was, I want this to be a movie that when frat guys go see it, they love it too," recalls director Nicholas Stoller (Forgetting Sarah Marshall).

Teddy "has all the power here," says Efron. "I think when he sees Seth's character he realizes how little he knows about life and what's coming up. The realization is frightening. I can relate a lot to that. It's scary."

The Rogen effect

Benediction from Rogen and Evan Goldberg, the producing/writing duo behind Pineapple Express, Superbad and This Is the End, could have a halo effect on Efron's future prospects, should Neighbors heat up the box office.

"Rogen's seal of approval will add immeasurable street cred to Efron," says Paul Dergarabedian, senior media analyst for box-office tracker Rentrak, who calls the young actor "at once charming and repellant, funny and endearing" in Neighbors.

Rogen laughs at the suggestion. "I think if the movie does well then that will happen, but if the movie fails it will do the exact opposite," he says. "I hope I legitimize him in some way — that would be nicer than ruining his chance of ever being in more comedies."

And for the first time, Efron's not concerned about the obvious camera play to his six-pack appeal.

Because it's partly the point.

Zac Efron goes shirtless in a scene from 'Neighbors.' "In this movie, a huge comic image to me was both Seth and Zac with their shirts off," says director Nick Stoller.(Photo: Glen Wilson, AP)

"In this movie, a huge comic image to me was both Seth and Zac with their shirts off," says Stoller. "(Efron) thought it was funny. He has a great sense of humor about his persona."

"It's like, (screw) it," says Efron, who in the past has found that "it sucks, it's confusing" and "there's something inherently wrong" with being asked to strip down in front of the lens. "This is the first time it makes sense, because we're making fun of it. I'm a douche. And that's cool. I love it."

"It's nice when you let the public know that you understand how you are perceived," says Rogen, whose famous friends sent their images up en masse in his 2013 apocalypse comedy This Is the End. "When I first met (Efron), I made a lot of assumptions about him, probably that he was going to be a brat or not self-aware. But he was actually very self-deprecating and charming and endearing."

Efron's been veering into adult territory since wrapping up vocally infused duties on career-launching projects like High School Musical and Hairspray. In the last two years, he's starred in (and produced) bro-friendly comedy That Awkward Moment, taken a dark turn in the ruthlessly brutal film noir, The Paperboy (in which Nicole Kidman famously urinated on him) and played a doctor in Parkland, a drama that retells the day John F. Kennedy was shot from multiple perspectives.

Neighbors could send him to the top of the class. While That Awkward Moment misfired with audiences and critics, "Neighbors is his comedy do-over that actually delivers the goods," says Dergarabedian.

Efron's still steering his career, having recently acquired the rights to John Grisham's The Associate. "I see it being somewhere between The Social Network and The Girl with the Dragon Tattoo." He pauses, chuckles. "And High School Musical."

Seth Rogen and Zac Efron on the set of 'Neighbors.'(Photo: Glen Wilson, Universal Pictures)

A sober take on life

What kind of neighbor is Efron? These days, a sober one. The actor has reshuffled priorities, relocating from his party pad in the Hollywood Hills to a more removed existence in Los Feliz.

Before, "I think I was the bad neighbor," he admits. "You know, I lived there when I was 21 to 26. We got our fair amount of noise complaints. Shouts through the fence. I never really dealt with cops, I never threw parties like that, police never showed up or anything like that. But there were a couple of times it just got out of hand."

And now?

"I'm much more subdued these days ... since Neighbors. I'm a lot more sedentary and chill," he says. "So there's less congregations, there's less parties at my house."

"If there is a moment in my life where everybody is pretty stoked about things right now, it's now,' says Efron, who recently completed rehab for drugs and alcohol.(Photo: Robert Hanashiro, USA TODAY)

Still, some press reports have been odd. Just two months ago, Efron and a friend were involved in a fight with a homeless man in a seedy area of Los Angeles in the middle of the night. "The wrong place at the wrong time," he says with a slight shrug, after telling The Hollywood Reporter the two had simply run out of gas looking for a bite to eat.

On set, Stoller said he didn't notice a strain on Efron if he confronted old demons playing Teddy. "I'm sure it was a little difficult for him, but I didn't notice anything," he says. "I had actually dealt with that before with Russell Brand on Get Him to the Greek. He literally was revisiting his dark, horrible past in that movie. And (Brand) just did it. ... Actors are there to be raw and real. A lot of them are fragile people for that reason."

Today, Efron says he is "completely sober," has joined Alcoholics Anonymous and is only in Los Angeles when he's working. "I don't really like to stay here that much anymore," he says. "That's the big thing that's changed. I travel a lot. If I don't have to be here, I'm not here."

Efron's blue eyes twinkle. "Believe me," he says, "if there is a moment in my life where everybody is pretty stoked about things right now, it's now. "

Zac Efron takes another step into the adult end of the acting pool playing a frat guy opposite Seth Rogen in the R-rated comedy "Neighbors." (Photo: Robert Hanashiro, USA TODAY)

Efron had a different sort of moment in the limelight last month while accepting the MTV Movie Awards' best shirtless performance for "That Awkward Moment." Efron arrived onstage wearing a shirt, but presenter Rita Ora relieved him of it. (Photo: Frederick M. Brown, Getty Images)

Taylor Schilling and Efron nuzzle in "The Lucky One," adapted from a Nicholas Sparks novel. He plays a Marine home from war searching for the woman he believes was his good luck charm. (Photo: Alan Markfield, Warner Bros.)